1. Field of the Invention
The present invention relates to a dipper stick, a part of an excavator, and more particularly to a dipper stick, made of polymeric composite materials such as a fiber reinforced plastics, capable of improving excavation capacity as a result of reducing its own weight, and reducing manufacturing processes therefor in comparison with conventional structural steel dipper sticks simultaneously with having an optimal strength.
2. Description of the Prior Art
As shown in FIG. 1 which is a perspective view of a conventional excavator having the dipper stick, the dipper stick 10 is a part hingewise connected at both ends thereof to a boom 2 and an excavating bucket 3, respectively, in order to be connected to and support them, said boom 2 adapted for supporting the excavating load. The dipper stick 10 is also connected to hydraulic cylinder actuators, a dipper cylinder 4 and a bucket cylinder 5, which cylinder 4 and 5 are telescopically actuated by a hydraulic controller (not shown) generally provided at the car body 1, thereby providing the excavating power for the excavating bucket 3. Therefore, the dipper stick 10 is necessarily subjected to the repeated intensive up-and-down and turning movement in accordance with the repeated telescopic motion of the hydraulic cylinders 4 and 5. In result, the dipper stick 10 is known as an intensive movement part together with the excavating bucket 3 so that the dipper stick 10 has to be manufactured of materials capable of providing a strength enough to withstand abrasion and mechanical shock encountered in the repeated excavating operation and support the excavation load.
Generally, known dipper sticks have been, therefore, manufactured of structural steels, for example SS41, to correspond to the above-mentioned mechanical conditions. However, the structural steel dipper stick has disadvantages in that it has a considerably heavy weight caused by the relatively larger specific gravity of the structural steels, 7.9 g/cm.sup.3, and a hollow box shaped and welded structure resulting in making the dipper stick be relatively weak for the outside mechanical shock, and also a weak resistance against the consume such as due to the repeated excavating operation and a weak resistance against corrosion such as due to atmosphere and moisture. Furthermore, the steel dipper stick in accordance with the prior art has the most serious disadvantage in that it needs relatively larger sizes of car body, relatively larger hydraulic power and lager necessary engine capacity for providing the desired practical excavation capacity of the excavator, caused by the above-mentioned heavy weight thereof.